1. Field of the Invention
The present invention relates to a process for preparing 2-carbamoyloxyalkyl-1,4-dihydropyridine derivatives and intermediates useful for the process. More particularly, the present invention relates to a process for the preparation of 2-carbamoyloxyalkyl-1,4-dihydropyridine derivatives which have pharmacological activities, and novel 3-amino-3-carbamoyloxyalkylacrylic acid derivatives and 3-carbamoyloxyalkylpropiolic acid derivatives which are useful as intermediates for the preparation of the dihydropyridine derivatives.
2. Discussion of the Background
2-Carbamoyloxyalkyl-1,4-dihydropyridine derivatives which have substituents with asymmetric structures at 2- and 6-positions of the dihydropyridine ring, are disclosed in Japanese Unexamined Patent Publications No. 118,565/1982 and No. 175,166/1982 by the present inventors. The dihydropyridine derivatives have coronary vasodilation activities or hypotensive activities and are expected to be useful as medicines for the treatment of disorders of circulatory organs.
Processes for the preparation of such asymmetric 1,4-dihydropyridine derivatives have been proposed in which 4-substituted acetoacetic acid esters, 4-substituted-2-ylideneacetoacetic acid esters or 4-substituted-3-aminocrotonic acid esters are used as the starting materials (Japanese Unexamined Patent Publications No. 5,777/1977 and No. 79,873/1978). However, these processes are not so efficient in that they involve a plurality of process steps to prepare the final products, i.e. the asymmetric 1,4-dihydropyridine derivatives, from the respective starting materials.